Much of the Wyoming rangeland could soon be inhospitable to deer, according to new research from ecologists at the University of Wyoming. The culprit: an invasive Eurasian prairie grass species called cheatgrass. The fast-growing, ever-thirsty species poses multiple problems for deer. Not only does it provide extremely low nutritional value, but it also siphons water away from native rangeland grasses, changing the composition of the prairies and pushing deer off their preferred habitat.
The study, published in the Rangeland Ecology & Management journal, found that mule deer increasingly avoid rangelands as the density of cheatgrass increases above 10 to 14%. Once cheatgrass makes up over 20% of the available forage, deer tend to avoid those specific areas altogether. Even more striking, though, the researchers estimate that over half of the study area—the Powder River and Pumpkin Buttes regions near Buffalo, Wyoming—could experience significant habitat degradation due to cheatgrass within the next 20 years, if it continues to expand at the same rate it has been.
Essentially, much of the Western range could soon hit a tipping point. Beyond being the threshold for deer preference, a rangeland that is over 20% cheatgrass also experiences significant ecological changes. Similar research in Nevada and Utah’s Great Basin region (an area known for mule deer hunting) has shown that once cheatgrass exceeds 20%, grassland communities—and subsequently deer habitat—begin to decline sharply in diversity, productivity, and overall biomass.
From there, it’s a vicious cycle. Cheatgrass grows earlier in the spring than native grasses, so by the time the natives sprout, the cheatgrass has already sucked much of the moisture out of the soil. The invader also dries out early in the summer, typically by mid-July, creating an elevated fire risk and a prairie full of unpalatable grasses. Not even pronghorn or livestock will touch the cheatgrass.
“Think about finding a dry piece of cardboard on the road, and you pick it up and eat it, and you find out it’s got broken glass in it and it cuts your mouth,” said Brian Mealor, one of the University of Wyoming researchers, in a 2020 story highlighting his work. “You might get something out of it, maybe there’s some protein hiding in that cardboard box, but it’s not palatable to begin with, and it causes actual physical damage if you bite it.”
Thus, the parched cheatgrass remains until a wildfire tears through—burning hotter and faster than usual thanks to the cheatgrass fuel—killing plants like sagebrush and bluebunch wheatgrass that deer rely on for winter-range survival. It also makes subsequent fires more likely.
Other regional research conducted in southern Idaho’s Snake River Plain by the U.S. Department of Agriculture shows that a cheatgrass-dominated rangeland burns far more frequently than a native grassland—to the tune of once every five years. Historically, before cheatgrass, the frequency is estimated to have been between 60 and 110 years.
But it’s not all doom and gloom, the Wyoming researchers say. Treating grasslands with herbicides—a chemical called “indaziflim” being the preferred option due to its multi-year efficacy following treatment—is surprisingly effective at restoring rangeland health and allowing native grasses a chance to repopulate. Researchers estimate that for every three hectares of grassland treated with herbicide for invasives, about one hectare can be transformed from habitat that mule deer avoid to habitat that they highly prefer.
That sounds great in theory, but the practicality of treating hundreds of thousands of acres with an herbicide is far more challenging. In a MeatEater interview last year with Jessie Shallow, a biologist with the Mule Deer Foundation, Shallow noted that projects targeting cheatgrass must hit at least around 12,000 acres to be effective. With one acre costing about $40, according to one estimate, the price tag adds up quickly.
For ranchers, though, it’s often worth the cost, as a cheatgrass invasion can devalue rangeland by $10 per acre per year. But for cash-strapped land management agencies like the Bureau of Land Management, which manages 18.4 million acres of land in Wyoming alone, it’s a more challenging cost-benefit analysis.
Already, state and federal agencies have allocated millions of dollars annually toward invasive grass treatments, but far more resources will be needed to make a significant impact, is the general consensus among the ecology community. “We manage it with money,” concludes Shallow. To make that happen, it’ll ultimately be up to the legislators, but it could have a big impact on the quality of deer hunting across the West.
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